1. Field of the Invention
The present invention relates generally to photovoltaic systems. The present invention relates more particularly to photovoltaic roofing systems in which photovoltaic elements are disposed upon roofing elements such as shingles, tiles, shakes or slates.
2. Summary of the Related Art
The search for alternative sources of energy has been motivated by at least two factors. First, fossil fuels have become increasingly expensive due to increasing scarcity and unrest in areas rich in petroleum deposits. Second, there exists overwhelming concern about the effects of the combustion of fossil fuels on the environment due to factors such as air pollution (from NOx, hydrocarbons and ozone) and global warming (from CO2). In recent years, research and development attention has focused on harvesting energy from natural environmental sources such as wind, flowing water, and the sun. Of the three, the sun appears to be the most widely useful energy source across the continental United States; most locales get enough sunshine to make solar energy feasible.
Accordingly, there are now available components that convert light energy into electrical energy. Such “photovoltaic cells” are often made from semiconductor-type materials such as doped silicon in either single crystalline, polycrystalline, or amorphous form. The use of photovoltaic cells on roofs is becoming increasingly common, especially as device performance has improved. They can be used to provide at least a significant fraction of the electrical energy needed for a building's overall function; or they can be used to power one or more particular devices, such as exterior lighting systems.
Existing photovoltaic modules do not blend well aesthetically with conventional roofs, appearing as bulky boxes on top of the roof. Photovoltaic roofing elements are being developed that integrate photovoltaic materials into roofing products, but these have their own attendant problems. For example, the photovoltaic elements used to make such photovoltaic roofing elements can fail, which can reduce the power-generating potential of the roof, and cause electrical inefficiencies that can reduce the effectiveness of the system much more than would be expected from the loss of a single photovoltaic element. Accordingly, it is generally necessary to replace photovoltaic roofing element when its photovoltaic cell fails. Similarly, wiring, contacts, and other electrical components can fail and require replacement. But the architecture of conventional photovoltaic roofing systems can make replacement of parts difficult, as the photovoltaic roofing elements are typically installed like traditional roofing elements, permanently affixed to the roof with fasteners that are protected from the elements under layers of material. There remains a need for systems that address these deficiencies.